The project im currently on is running high in the polycount numbers and with edge faces on the frame rate drops dramatically... I use a combination of "Shaded+Edged Faces" in the view port when modeling. The same number of polys on screen with edge faces off is fine, but when I enable edge faces frame rate drops...anyone…
Shaded+Edged Faces should be 2 rendercalls, the scene has to be rendered twice, once for the solid part and a backface culled wireframe one on top, at least that´s how it´s often done.
This is not a matter of turning it off or on, this is what happens under the hood when you use hidden line or Solid/shaded + edged faces. Edit: I didn´t mean backface culling , i meant it renders the wireframe on top with single sided rendering. And it´s just a little bit slower, not unmanagable ;)
If you are using Direct X (instead of Nitrous) make sure that Anti-Alias wireframe views is turned off. Historically, wireframe and edged face views have been slower for me than just shaded views. I think if you have an Nvidia Quadro or an ATI FirePro, you don't suffer from this issue.